Apparently Ms.Marvel is in the Avengers trailer, she is the third mystery woman in Tony's apartment. According to the leaked video of Cap and Tony arguing and chopping wood, it was discovered that Hawkeye has a farm. That the reason we get to see Loki and Heimdall, is that Thor saw some sort of vision thanks to Ms.Maximoff and went off to get information. Apparently the brief frame we see of Cap in the 40's is probably the same thing, also something about the ballerinas and Black Widow. These are just theories though, so we'll see.